With regard to tougher emissions regulations, there is a constant demand for shaft seals with lower friction to seal the crankshaft. At the same time, sufficient stability of the shaft seal against vacuums and excess pressure in the engine occurring during operation must be ensured; for example, in modern petrol engines, considerable vacuums can occur in the crankcase. In the past, radial shaft seals which are optimised in terms of friction were used to seal the crankshaft, wherein the pressure stabilisation was achieved by suitable geometry of the sealing lip. However, the friction reduction able to be achieved with radial shaft seals is limited.
A mechanical seal for sealing the crankshaft is known from DE 10 2011 114 349 A1 Mechanical seals are very low in friction in general, but consist of a relatively high number of individual parts, require much installation space and are comparatively expensive.
An axial shaft seal is known from FIG. 5 of DE 103 34 896 A1. In the case of this shaft seal, a reliable seal is achieved by three tangential sealing elements, in particular a tangential dust seal, a tangential buffer seal and a sealing collar, but at the price of increased friction.
The axial shaft seal according to EP 2 749 796 A1 also has a dust lip which is supported in a sealing manner on the race over an axial length and which indeed causes a sufficient level of imperviousness to dust, but in turn leads to increased friction. Additionally, the sealing element only has low stability against a vacuum, as the sealing lip is folded back from the race in the case of an engine-side vacuum, due to a weakness close to its connection to the stiffening section, and then completely loses the sealing functionality.
Document U.S. Pat. No. 4,928,979 discloses a shaft seal to seal a shaft against a housing.